1. Field of the Invention
The invention relates to a magnetic head and, more specifically, to a magnetic head used in a magnetic recording/reproducing apparatus such as a video tape recorder (VTR), and a digital audio tape recorder (DAT).
2. Description of the Background Art
Recently, density of recording signals have come to be increased in magnetic recording/reproducing apparatuses such as VTRs and DATs. Corresponding to the higher density recording, metal tapes having higher coercive force using ferromagnetic metal powder such as Fe, Co or Ni as magnetic powder have come to be used. For example, in a compact VTR called a 8 mm video tape recorder, a metal tape having coercive force as high as about Hc=1400 to 1500 oersted is used. The reason for this is that a recording media capable of shortening recording wavelength of signals have been desired, in order to increase recording density to reduce the size of the magnetic recording/reproducing apparatus.
When a conventional magnetic head formed only of ferrite is used for recording on the metal tape, performance of the metal tape cannot be fully exhibited, since magnetic saturation phenomenon occurs as saturation flux density of ferrite is about 5500 gauss at the highest. A magnetic head corresponding to a metal tape having high coercive force must satisfy the following conditions required for a magnetic head, that is, high-frequency characteristics and high wear resistance of the magnetic core as well as higher saturation flux density near a gap of the magnetic core. A magnetic head (called a composite type magnetic head) used for the metal tape satisfying these conditions has been proposed in which a portion near the magnetic gap, where magnetic saturation phenomenon tends to occur most frequently, is formed by a metal magnetic material (for example, permalloy, sendust, amorphous magnetic material) having higher saturation flux density than that of ferrite used for magnetic cores. The composite type magnetic head has superior reliability, magnetic characteristics and wear resistance.
FIG. 10 is a perspective view showing appearance of a conventional magnetic head, and FIG. 11 shows a tape contact surface of the magnetic head of FIG. 10. In the conventional magnetic head, ferromagnetic metal thin films 3a and 3b formed of sendust or the like having high saturation flux density are provided near a magnetic gap 2 consisted of a pair of magnetic core halves 1a and 1b of ferromagnetic oxide such as Mn-Zn ferrite facing to each other with a non-magnetic material posed therebetween. The magnetic core halves 1a and 1b are joined by glass 4 with a coil groove 5 being provided. In the magnetic head, the boundaries 6a and 6b between the magnetic core halves 1a and 1b and the ferromagnetic metal thin films 3a and 3b are in parallel with the direction of track width of the magnetic gap 2.
FIG. 12 is a perspective view showing an appearance of another example of a conventional composite type magnetic head, and FIG. 13 shows the tape contact surface of the magnetic head. In this magnetic head, the boundaries 6a and 6b between the magnetic core halves 1a and 1b and the ferromagnetic metal thin films 3a and 3b are inclined and not in parallel with the forming surface of the magnetic gap 2. It is a structure of a composite type magnetic head proposed to prevent bad influences of a possible pseudo gap to the performance of the magnetic head.
Generally, in the magnetic heads shown in FIGS. 12 and 13, the track width of the magnetic gap 2 is related to the film thickness of the ferromagnetic metal thin films 3a and 3b. Therefore, the thickness of the ferromagnetic metal thin films 3a and 3b is about 20 to 30 .mu.m. Meanwhile, in the magnetic head shown in FIGS. 10 and 11, the track width of the magnetic gap 2 is not related to the thickness of the ferromagnetic metal thin films 3a and 3b, so that the thickness of the ferromagnetic metal thin films 3a and 3b is as thin as 5 .mu.m. Accordingly, the magnetic head of FIG. 10 is superior in production yield and cost efficiency compared with that shown in FIG. 12. However, magnetic saturation tends to occur in low frequency region during recording since the ferromagnetic metal thin films 3a and 3b are thin in the magnetic head of FIG. 10, so that the self recording/reproducing capability in low frequency region is low.
Japanese Patent Laying-Open No. 62-177714 discloses a magnetic head in which gap length is changed in recording and reproducing by providing a magnetic thin film having saturation flux density of 500 gauss or less at the gap junction surface of the pair of magnetic core halves, in order to improve recording efficiency to a magnetic tape having high coercive force. However, in this magnetic head, saturation occurs even at a small flux as the saturation flux density of the magnetic thin film is as small as 500 gauss or less, which enlarges the substantial gap length, and therefore it was difficult to effectively reproduce high frequency signals.